The evaluation of calcium channel blocking drugs, Verapamil, Diltiazem, Nifedipine and Lidoflazine, on platelet aggregation indicated an inhibitor by Verapamil and Dilitiazem to aggregation by epinephrine. Further evaluations of cyclic AMP levels indicated that Diltiazem appears to increase platelet levels of cAMP whereas Verapamil does not. Competitive binding studies are in progress to assess Alpha adrenergic receptor interactions with these drugs. Dantrolene will be studied with the Quin-2 method for monitoring internal calcium levels in platelets. Cyclic AMP levels in response to Vanadate and Ristocetin will also be evaluated.